The present invention generally relates to optical systems, and more particularly to micro-positioning optical systems that have an optical element that can be moved or positioned relative to an optical source or receiver.
It is desirable in many applications to precisely align or micro-position various objects. Although the precision with which the objects must be positioned varies according to the application, the objects must often be aligned to within several microns to several tenths of microns. One typical application that can benefit from micro-positioning relates to the alignment of an optical fiber, such as a single mode optical fiber, with another electro-optical element, such as a laser diode or Vertical Cavity Surface Emitting Laser (VCSEL). By appropriately micro-positioning the electro-optical device with the optical fiber, a large percentage of the optical signal can be coupled to the respective optical fiber.
Although several micro-positioning devices have been proposed for fiber optic connector applications, a need still exists for fiber optic alignment devices that incorporate improved micro-positioning techniques. For example, increased demands are being made upon the precision with which objects, such as optical fibers, are aligned. As such, there is a need for more precise alignment devices that provide reliable and repeatable micro-positioning to within a few microns to several tenths of microns.
Another application that can benefit from micro-positioning is optical switching. Recent developments in information networks have provided an increased demand for optical communication systems capable of transmitting a great deal of data. In one example, free-space optical interconnection is now being used to make relatively short but fast interconnections within data processing or communications systems. Some of the advantages of free-space interconnects include direct interconnects between circuit boards, arbitrary interconnection patterns, multiple fan-outs, channel isolation and increased bandwidth.
Optical switches typically switch, or redirect, light from for example, an electro-optical device such as a VCSEL to one of several optical receivers. The optical receivers can be optical fibers, Resonant Cavity Photo Detectors (RCPD""s), or any other type of optical receiver. Some optical switches use lens decentering to steer the light beam as desired. See, for example, xe2x80x9cMEMS-Controlled Microlens Array For Beam Steering and Precision Alignment in Optical Interconnect Systemsxe2x80x9d, Tuantranont et al., Solid-State Sensor and Actuator Workshop, Hilton Head Island, S.C., Jun. 4-8, 2000(pp. 101-104).
Yet another application that can benefit from micro-positioning is optical scanning devices used to read and/or write CDs or the like. Micro-positioning can be used to improve the alignment of the optical scanning devices relative to the tracks of the CD. All of the above applications and others could benefit from an improved micro-positioning system.
The present invention provides an improved micro-positioning system that can accurately position an optical element relative to an optical device such as a laser diode, a Vertical Cavity Surface Emitting Laser (VCSEL), a Resonant Cavity Photo Detector (RCPD), or other type of optical device. The optical element may be any type of optical element including, for example, a lens, a filter such as a diffraction grating, or other type of optical element.
In one illustrative embodiment, a micro-positioning system is provided that selectively moves the optical element independently in both the X and Y directions relative to a base. The base is preferably fixed relative to an optical device, such as a VCSEL, RCPD or photo diode. Thus, in one embodiment, the optical element can be independently moved in both the X and Y directions relative to the optical device.
Independent movement of the optical element is preferably provided by a carrier that is spaced above the base. The carrier is operatively coupled to the base such that the carrier can be selectively moved in the X direction but not substantially in the Y direction. The optical element is then preferably operatively coupled to the carrier such that the optical element can be selectively moved in the Y direction relative to the carrier, but not substantially in the X direction. An X driver is then used to selectively move the carrier in the X direction relative to the base, and a Y driver is used to selectively move the optical element in the Y direction relative to the carrier. The carrier can thus be used to provide independent movement of the optical element in both the X and Y directions relative to the base.
Preferably, the X driver and the Y driver provide movement by means of an electrostatic force. In one embodiment, the X driver includes a number of inter-digitated comb fingers. Some of the comb fingers are mechanically coupled to the carrier while others are mechanically coupled to the base. By providing a voltage difference between the comb fingers, the X driver can xe2x80x9cpullxe2x80x9d the carrier in one direction (e.g., left) relative to the base. Another set of comb fingers may be provided on the opposite side of the carrier to xe2x80x9cpullxe2x80x9d the carrier in the opposite direction (e.g., right), if desired. Likewise, the Y driver may include a number of inter-digitated comb fingers. Some of the comb fingers are mechanically coupled to the carrier while others are mechanically coupled to the optical element. By providing a voltage difference between the comb fingers, the Y driver can xe2x80x9cpullxe2x80x9d the optical element in one direction (e.g., up) relative to the carrier. Another set of comb fingers may be provided on the opposite side of the carrier to xe2x80x9cpullxe2x80x9d the optical element in the opposite direction (e.g., down), if desired.
The optical element may be any type of optical element, such as a lens, an optical filter such as a diffraction grating, an optical polarizer, or any other type of optical element. The optical element preferably has at least two regions where the optical characteristics are different in the at least two regions. In one example, the optical element may be a lens. The optical characteristics of a lens typically vary across the lens. Thus, a light beam that intersects the lens at a first location will be refracted at a different angle than a light beam that intersects the lens at a second location. In another example, the optical element may include a diffraction grating that has a grating spacing and a grating width. The grating spacing and/or grating width may be different in different regions of the optical element. Alternatively, or in addition, the angle of the diffraction grating may be different in different regions of the optical element.
In operation, the optical element may be selectively moved so that a light beam intersects a selected region of the optical element. Because the optical characteristics of the optical element are different in different regions, the optical element produces different optical results as the light beam is moved between regions. For example, when the optical element is a lens, the light beam is refracted at different angles and thus to different locations as the lens is moved relative to the light beam. This is sometimes referred to as beam steering. Beam steering can be useful in a number of applications, including optical alignment, optical switching including Space Division Multiplexing (SDM), and other applications.
In another example, when the optical element includes a diffraction grating with regions having different grating spacing and/or different grating widths, the light beam may be selectively separated or filtered according to wavelength. This may be useful in providing, for example, Wavelength Division Multiplexing (WDM) or the like. Likewise, when the angle of the diffraction grating is varied in different regions of the optical element, the polarization of the light beam may be controlled. This can be useful in providing Polarization Division Multiplexing (PDM).